Method and apparatus for prolonging the life of electric brushes



NOV. 20, 1945. v SHOBERT 2 2,389,214

METHOD AND APPARATUS FOR PROLONGING THE LIFE OF ELECTRIC BRUSHES Filed Sept. 24, 1941 INVENTOR. Maw ,1- BY [87%,6MWW

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Patented Nov. 20, 1945 METHOD AND APPARATUS Foit PROLONG- mo THE LIFE or ELECTRIC nnusnas Eric I. Shobert, H, St. Marys, Pa., assignor to Stackpole Carbon Company, St. Marys, Pm, a corporation of Pennsylvania Application September 24, 1941, Serial No. 412,134

8 Claims.

Thi invention relates to a method and app ratus for prolonging the lives of electric brushes used for engagin slip rings or the commutators of generators and motors under conditions of low atmospheric pressure or low absolute humidity.

It is known that the electric brushes of genorators. motors and the like wear out much more rapidl when the surrounding atmosphere has a low absolute humidity or a low pressure or both. The reason for this is not entirely clear, but I believe that it is due to the following factors. Under ordinary pressures and humidity there is a layer of moist air on the commutator or slip ring such as is present on all stationary surfaces. This layer of air serves as a lubricant for the contact surface of the brush and is removed from the commutator as it passes under the brush.

However, a similar film of air forms upon the commutator again before any given area of its contact surface returns to the brush. If the air pressure is low or if the humidity is low there is not enough air and moisture adsorbed on the contact surface of the commutator to build up this film again before any given area of the commutator reaches the brush.

This is an especially serious problem in connection with generators and motors used at high altitude in airplane service where the rate of wear is many times faster than that found at ordinary pressure and humidities. For example, at 40,000 feet it has been found that brushes Will wear out completely in approximately hours while at ground level the same brushes will last 500 to 1000 hours. This involves a great deal of maintenance for equipment used at high altitudes. The same problem also exists on generator and motor equipment in climates and under atmospheric conditions where the absolute humidity is Very low.

It is among the objects of this invention to provide apparatus for decreasing brush wear which is simple and inexpensive, readily attached to a brush, free of upkeep cost and which increases theair pressure and humidity adjacent the brush without the use of additional operating means. Another object is to provide a method of prolonging the lives of electric brushes.

In accordance with this invention an air defleeting member is mounted adjacent an electric brush engaging a commutator or the like, and projects from the entering side of the brush by which is meant the side from which the commutator rotates across the brush. This deflecting member intercepts the air that is carried along by the rotating commutator and directs it in fixed position in any suitable manner.

inwardly against the contact surface of the commutator in the area where it starts to engage the brush. The deflector member is so constructed that it narrows the stream 01' air as it approaches the brush so that its pressure and turbulence are increased. Preferably, the deflector member or supercharger has an outer wall more or less tangential to the commutator and side walls that extend inwardly substantially into engagement with the commutator. The outer end of the deflector is open so that the thin layer of air that travels with the commutator and the air drawn along by it may enter the deflector and thus be guided to the brush.

The preferred embodiment of the invention is illustrated in the accompanying drawing in which Fig. 1 is an end view of the armature of an electric motor or g n r t 2 s a side view of the commutator; and Fig. 3 is a perspective view of a brush holder with my supercharger attached.

Referring to Figs. 1 and 2 of the drawing, a motor or generator is provided with the usual commutator I encircling the armature shaft 2. Engaging the commutator at diametrically opposite points are electric brushes 3 of carbon or the like which are connected by wires 4 in an electric circuit. Each brush is slidably mounted in a hollow rectangular holder 5 that is supported The brushes are pressed against the commutator by springs, not shown. Thus far the construction is conventional.

It is a feature of this invention that when this motor or generator is used under low pressures or low humidities the brushes last substantially I as long as under normal pressures and humidities.

Accordingly, a bracket 1 is attached by screw 8 to the side of each brush holder on the entering side of the brush. Each bracket is L-shaped with a flat arm that extends at right angles away from the adjoining brush holder. or commutator side of the projecting bracket arm is the supercharger that is the subject of this invention. This supercharger is either insulated from the brush or is made from suitable insulating material, such as Bakelite. The supercharger is of general U-shape in cross-section and preferably has a flat outer wall 9 held against the bracket by screws l0 and extending inwardly under the brush holder to a point almost in contact with the brush with its inner edge in contact, or substantially so, with the commutator.

Extending inwardly toward the commutator from the opposite side edges of the superchargers outer wall 9 is a pair of laterally spaced side walls Secured to the inner I! the inner edges of which are curved to conform to the surface of thecommutator .with which they are substantially in engagement, as shown in Fig. 1. the supercharger and the commutator a channel open at its outer end and decreasing in width as it approaches the brush. The inner portions of the slots l8 between the segments of the coinmutator are filled with mica or the like as is the usual practice. As the purpose of the supercharger is to guide a stream or air in toward the brush and commutator, the open outer portions slots II are plugged so that the air stream can not escape through them around the inner edges of side walls '2 from inside of the supercharger. For this purpose an insulating cement l4 may be used which extends far enough inwardly in the slots to pass under side walls l2 oi the supercharger but not far enough to be in the path or the brush.

When the commutator rotates, a thin layer of air adheres to it and rotates with it. This air is therefore carried into the open outer end of the supercharger. In addition, this thin layer of air carries along with it by friction some of the surrounding air and thus draws the latter into the supercharger with it. As the size of the passage in the supercharger decreases as it approaches the brush, the stream of air that has entered it becomes compressed and extremely turbulent by the time it reaches the inner end of the passage. By properly proportioning the size and shape of the supercharger passage and the rate at which it is narrowed, it is possible to obtain whatever pressures are desired. It will be obvious that the supercharger need not be fastened to brush holder 5, but that it can be held against the commutator in any other suitable manner, such as under spring pressure in its own holder similar to holder 5.

The great turbulence of the air next to the commutator at the entering edge-of the brush permits substantially all the moisture in it to be adsorbed on the contact surface of the commutetor. The increased air pressure at the inner end o! the supercharger passage causes this turbulence to take place close enough to the commutator surface for the adsorption to occur most efiectively and rapidly. To be most effective, the turbulence should take place within .010 inch of the commutator. Also, increasing the air pressure results in compressing more moisture into a given volume of air so that its absolute humidity, as well as its relative humidity, is increased. The net result is that the rate of brush wear with the supercharger attached is substantially the same regardless of whether the pressure and humidity of the atmosphere are high or low.

In tests run on a generator not equipped with my supercharger it was found that a brush were away mils during 24 hours-use at an absolute humility of from 5 to 6 grains per cubic foot. At 1 grain per cubic foot the rate of wear was mils in 24 hours. The supercharger was then placed on the generator and the test continued and the rate of wear was found to be from 4 to 5 mils for 24 hours at-l grain per cubic foot, the same rate of wear. as previously occurred at from 5 to 6 grains per cubic foot. With the supercharger the rate of wear remained at from 4 to 5 mils for 24 hours at an absolute humidity of from 5 to 6 grains per cubic foot.

According to the provisions of the patent statutes, I have explained the principle and construction of my invention and have illustrated and There is thus formed between described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of prolonging the life of an electric brush engaging a rotating conductor in electrical apparatus, comprising intercepting air carrled along by the motion of said conductor and directing it through a progressively narrowing channel to the contact surface of the conductor in the area where it starts to engage the brush, whereby the pressure and turbulence of the air are increased in said area.

2. In electrical apparatus the combination with a rotatable cylindrical conductor and an electric brush contacting it, of means mounted adjacent the entering side of the brush for intercepting air carried along by the motion of said conductor and compressing said air and directing it against the contact surface orsaid conductor where it starts to engage the brush.

3. In electrical apparatus the combination with a rotatable cylindrical conductor and an electric brush contacting it, of an air deflecting and conducting member extending away from the entering side of the brush and having laterally spaced side walls substantially engaging said conductor; whereby a stream of air enters the outerend of said member and is directed thereby against the contact surface of the conductor where it starts to engage the brush.

4. In electrical apparatus the combination with a rotatable cylindrical conductor and an electric brush contacting it, of an air deflecting and conducting member extending away from the entering side of the brush and being of general U-shape in transverse section with its side edges substantially engaging said conductor, whereby a stream of air enters the outer end of said member and is directed thereby against the contact surface of the conductor where it starts to engage the brush.

5. In electrical apparatus the combination with a rotatable cylindrical conductor and an electric brush contacting it, 01' an air deflecting and conducting member having an outer wall projecting tangentially of said conductorfrom the entering edge of the contact face of the brush, said member having laterally spaced side walls extending inwardly substantially into engagement with said conductor, whereby a stream of air enters the outer end of said member and is directed thereby against the contact surface of the conductor where it starts to engage the brush.

6. In electrical apparatus the combination with a rotatable cylindrical conductor and an eiectric brush contacting it, of means mounted adjacent the entering side of the brush for intercepting air carried along by the motion of said conductor, said meansforming with the conductor a progressively narrowing channel terminating at its inner end adjacent the entering edge of the brush, whereby said intercepted air is compressed and directed against the contact surface of the conductor.

7. In electrical apparatus, the combination with a rotatable cylindrical conductor, and an electric brush mounted in a brush holder and contacting the conductor, of a bracket attached to the brush holder on the entering side of the brush and projecting away from it at right angles to the brush, and an air deflecting and conducting member attached to the inner side of the bracket and formed to receive and directs, stream of air against the contact surface of the conductor where it starts to engage the brush.

8. The combination with a commutator having segments separated by circumferentially spaced slots, and an electric brush contacting the commutator, of an air deflecting and conducting member extending away from the entering side 

